Seatbelt apparatus

ABSTRACT

A seatbelt apparatus ( 15 ) includes a seatbelt ( 14 ) for restraining an occupant ( 10 ) in a seat ( 13 ) of a vehicle, an actuator ( 29 ) for tightening the seatbelt ( 14 ) at various levels of tension and for loosening the seatbelt ( 14 ), plural collision prediction devices ( 38, 39 ) for predicting occurrence of a collision, and a control device ( 35 ) for controlling the actuator ( 29 ) so as to exert one of the various levels of tension on the seatbelt ( 14 ) depending on the prediction results by the collision prediction devices ( 38, 39 ).

FIELD OF THE INVENTION

The present invention relates to a seatbelt apparatus in which aseatbelt may be tightened using an actuator such as an electric motor.

DESCRIPTION OF RELATED ART

A technical means for a seatbelt apparatus in which a seatbelt may betightened using an electric motor as an actuator is disclosed inJapanese Patent No. 2946995, in which a seatbelt is tightened byexerting a first tension thereon using a pretensioner having an electricmotor when a collision of the vehicle is predicted, and the seatbelt istightened by exerting a second tension, which is greater than the firsttension, thereon using an explosive pretensioner when a collision of thevehicle is detected.

In the seatbelt apparatus disclosed in the above-mentioned patentdocument, because tension is exerted on the seatbelts based on aprediction that there may be a collision with a moving object in frontof the vehicle or a moving vehicle in front of the vehicle so thatoccupants are restrained in the seats by the seatbelts, the seatbeltapparatus must be configured beforehand so as to be able to exert greatamounts of tension on the seatbelts in order to ensure tightening of theseatbelts. Due to progresses made in radar technology in recent years,irregularities in the road can also be detected, and as a result, theoccupants may experience unnecessary unusual sensations due to greatamounts of tension exerted on the seatbelts even when there is lowprobability of collision.

DISCLOSURE OF THE INVENTION

In view of the above circumstances, an object of the present inventionis to provide a seatbelt apparatus in which, when a collision ispredicted and occupants are to be restrained in their seats, an optimumamount of tension can be exerted on the seatbelts depending onprediction results for a collision.

In order to achieve the above objects, the present invention provides aseatbelt apparatus including: a seatbelt for restraining an occupant ina seat of a vehicle; an actuator for tightening the seatbelt at variouslevels of tension and for loosening the seatbelt; plural collisionprediction devices for predicting occurrence of a collision; and acontrol device for controlling the actuator so as to exert one of thevarious levels of tension on the seatbelt depending on the predictionresults by the collision prediction devices.

According to the above seatbelt apparatus, because the control deviceexerts one of the tensions of differing amounts in the seatbeltdepending on the prediction results by the collision prediction devices,it is possible to exert great amounts of tension on the seatbelt so asto strongly tighten the seatbelt when probability of collision is high,and to exert a small amount of tension on the seatbelt so as tomoderately tighten the seatbelt when probability of collision is low.

In the above seatbelt apparatus, the collision prediction devices mayinclude at least two of a stationary object collision prediction devicefor predicting occurrence of a collision with a stationary object, amoving object collision prediction device for predicting occurrence of acollision with a moving object, and a brake operation collisionprediction device for predicting occurrence of a collision based on anoperation of the brake of the vehicle.

According to the above seatbelt apparatus, because the collisionprediction devices include at least two of a stationary object collisionprediction device for predicting occurrence of a collision with astationary object, a moving object collision prediction device forpredicting occurrence of a collision with a moving object, and a brakeoperation collision prediction device for predicting occurrence of acollision based on an operation of the brake of the vehicle, the controldevice can exert an optimum amount of tension on the seatbelt dependingon the prediction results predicted by the collision prediction devices.

In the above seatbelt apparatus, the collision prediction devices mayinclude a stationary object collision prediction device for predictingoccurrence of a collision with a stationary object, a moving objectcollision prediction device for predicting occurrence of a collisionwith a moving object, and a brake operation collision prediction devicefor predicting occurrence of a collision based on an operation of thebrake of the vehicle, and the :control device may be adapted to exert agreater amount of tension on the seatbelt when occurrence of a collisionis predicted by the moving object collision prediction device and whenoccurrence of a collision is predicted by the brake operation collisionprediction device than when occurrence of a collision is predicted bythe stationary object collision prediction device.

According to the above seatbelt apparatus, because the control device isadapted to exert a greater amount of tension on the seatbelt whenoccurrence of a collision is predicted by the moving object collisionprediction device and when occurrence of a collision is predicted by thebrake operation collision prediction device than when occurrence of acollision is predicted by the stationary object collision predictiondevice, when irregularities in the road, which are frequently detectedas stationary objects in a normal travel of a vehicle, are detected,i.e., when probability of collision is low, a small amount of tension isexerted on the seatbelt, and when a moving object at a short distance,which is less frequently detected in a normal travel of a vehicle, isdetected, i.e., when probability of collision is high, a great amount oftension is exerted on the seatbelt.

In the above seatbelt apparatus, the control device may be adapted totemporarily increase electric current supplied to the actuator at thebeginning of controlling of the actuator for exerting tension on theseatbelt.

According to the above seatbelt apparatus, because the control device isadapted to temporarily increase electric current supplied to theactuator at the beginning of controlling of the actuator for exertingtension on the seatbelt, the operation of the actuator can beaccelerated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing the general construction of an embodiment ofa seatbelt apparatus and an associated system according to the presentinvention.

FIG. 2 is a time-domain chart showing electric current supplied to amotor during a warning mode in an embodiment of the seatbelt apparatusaccording to the present invention.

FIG. 3 is a time-domain chart showing tension exerted on the seatbeltduring a warning mode in an embodiment of the seatbelt apparatusaccording to the present invention.

FIG. 4 is a time-domain chart showing electric current supplied to themotor in an embodiment of the seatbelt apparatus according to thepresent invention when occurrence of a collision with a moving object ispredicted or when occurrence of a collision is predicted based on anoperation of the brake.

FIG. 5 is a time-domain chart showing electric current supplied to themotor in an embodiment of the seatbelt apparatus according to thepresent invention when occurrence of a collision with a stationaryobject is predicted.

FIG. 6 is a time-domain chart showing various operations and degree ofdeceleration in an embodiment of the seatbelt apparatus according to thepresent invention.

PREFERRED EMBODIMENTS OF THE INVENTION

An embodiment of a seatbelt apparatus according to the present inventionwill be explained below with reference to the appended drawings.

As shown in FIG. 1, a seatbelt apparatus 15 according to the presentembodiment, which restrains an occupant 10 using a seatbelt 14, isprovided with a seat 13 that includes a seat cushion 11 for mainlysupporting the buttocks of the occupant 10, and a seatback 12 for mainlysupporting the back of the occupant 10. The seatbelt apparatus 15 inthis embodiment provided with the seat 13 includes a so-calledthree-point seatbelt device.

In the seatbelt apparatus 15, a webbing 21 of the seatbelt 14 extendsupward from a retractor 20 which is provided on a center pillar or thelike (not shown) that is located at the outside in the compartment withrespect to the seat 13, and runs through a through anchor 22 which issupported an upper portion of the center pillar. An end of the webbing21 is attached to the vehicle floor via an outer anchor 23 which islocated at the outside in the compartment with respect to the seat 13.The seatbelt 14 is provided with a tongue plate 25 through which aportion of the webbing 21 positioned between the through anchor 22 andthe outer anchor 23 runs. The tongue plate 25 is made engageable withand disengageable from a buckle 26 which is attached to the vehiclefloor at the inside in the compartment with respect to the seat 13.

When the seatbelt 14 is drawn out from the retractor 20 by being drawnat the tongue plate 25 by the occupant: 10 seated in the seat 13, andthe tongue plate 25 is engaged with the buckle 26, a portion of theseatbelt 14 from the through anchor 22 to the tongue plate 25 mainlyrestrains a portion of the occupant 10 from the shoulder to the chest onthe side opposite to the seat 13, and a portion of the seatbelt 14 fromthe tongue plate 25 to the outer anchor 23 mainly restrains the abdomenof the occupant 10 on the side opposite to the seat 13.

The retractor 20 is provided with a first pretensioner 28 which is awell-known and irreversible explosive pretensioner for instantlyretracting the seatbelt 14 using an explosive force of an explosive, oralternatively, an irreversible spring type pretensioner.

The retractor 20 is also provided with a reversible second pretensioner30 for retracting and tightening the seatbelt 14 using drive power of anelectric motor 29. More specifically, in the second pretensioner 30, areel 31, which is housed in the retractor 20 for winding the webbing 21,on the one hand, enforcedly winds and draws the seatbelt 14 by beingrotatably driven by the electric motor 29, and on the other hand, themechanical engagement of the reel 31 with the electric motor 29 isdisengaged so as to make the reel 31 idle and be driven by a spring, andthereby tightening of the seatbelt 14 released so that the seatbelt 14is relaxed. The construction of the retractor 20 is not shown because itis well-known. Alternatively, the electric motor 29 may be a motor whichis capable of performing normal rotation and reverse rotation, and theelectric motor 29 may be operated such that the seatbelt 14 is tightenedby the normal rotation, and the seatbelt 14 is relaxed by the reverserotation.

To the electric motor 29, a control unit for controlling the operationof the electric motor 29, i.e., an electrical seatbelt control unit 35is connected. The electrical seatbelt control unit 35 is connected to aconnection bus 36 of an inter-vehicle LAN and controls the electricmotor 29 in such a manner that the seatbelt 14 is drawn taut so as torestrain the occupant 10 when occurrence of a collision with an objectin front of the vehicle is predicted, and that the mechanical engagementof the reel 31 housed in the retractor 20 with the electric motor 29 isautomatically disengaged when the prediction of a collision iscancelled.

To the connection bus 36, a brake control unit-38 for sending out abrake signal indicating a possibility of a collision based on anoperation of the brake, a radar control unit 39 for sending out a signalindicating a possibility of a collision with an moving object such as avehicle and a signal indicating a possibility of a collision with astationary object such as an obstacle, and a vehicle speed measuringunit 40 for measuring vehicle speed are connected.

Moreover, to the electrical seatbelt control unit 35, an airbag controlunit 43 for controlling a supplementary restraint device including anairbag is connected.

The brake control unit 38 sends a signal indicating a possibility of acollision (a BA signal) to the electrical seatbelt -control unit 35 whena pressing rate of the brake pedal exceeds a threshold which isdetermined depending on the current vehicle speed.

The BA signal may be sent out when a dangerous operation to the vehicle,such as a quick steering operation, is detected.

The BA signal may be sent out when a dangerous state of the vehicle isdetected, for example, when slip of the wheel is detected based on adifference between the rotational speeds of the right and left wheels.

The radar control unit 39 detects an object in front of the vehicleusing a radar. The radar control unit 39 determines that there is apossibility of a collision when the relationship between the object andthe vehicle (e.g., distance, relative velocity, etc.) satisfiespredetermined conditions, and determines that there is no possibility ofa collision when the relationship does not satisfy predeterminedconditions. In the present invention, prediction of occurrence of acollision is executed with regard to not only in front of the vehicle,but also behind the vehicle, and the right and left of the vehicle.

The radar control unit 39 detects, for example, an object in front ofthe vehicle using the radar, and the radar control unit 39 determineswhether the object is a stationary object or a moving object based onthe relative velocity between the object and the vehicle, or the like,when it is determined that the distance between the object and thevehicle is decreased to less than a predetermined value based on theradar signals.

When it is determined that the object with which a collision ispredicted is a stationary object, the radar control unit 39 sends astationary object signal indicating a possibility of a collision with astationary object to the electrical seatbelt control unit 35. On theother hand, when it is determined that the object with which a collisionis predicted is a moving object, the radar control unit 39 sends amoving object signal indicating a possibility of a collision with amoving object to the electrical seatbelt control unit 35.

The vehicle speed measuring unit 40 sends a vehicle speed signal, whichis output from a vehicle speed sensor, to the electrical seatbeltcontrol unit 35.

To the airbag control unit 43 for controlling the airbag, a buckleswitch 45, which detects whether the tongue plate 25 provided on theseatbelt 14 of the seatbelt apparatus 15 is engaged with the buckle 26,i.e., whether the seatbelt 14 is worn, is connected. Moreover, to theairbag control unit 43, a warning lamp 48 installed in an instrumentboard 47 provided in an instrument panel pad is connected. In addition,a crash sensor 49 is connected to the airbag control unit 43.

A buckle signal output from the buckle switch 45 is sent to theelectrical seatbelt control unit 35 via the airbag control unit 43. Whenthe seatbelt apparatus 15 has a failure, the electrical seatbelt controlunit 35 notifies the occupant 10 of the failure by lighting the warninglamp 48 using the airbag control unit 43.

The electrical seatbelt control unit 35 of the seatbelt apparatus inthis embodiment controls the electric motor 29 so as to exert tensionand tighten the seatbelt 14 depending on prediction results obtained bythe brake control unit 38 and the radar control unit 39 for performingprediction of a collision of the vehicle. The electrical seatbeltcontrol unit 35 applies a tightening operation to the seatbelt 14 at theearliest instance among when a collision with a stationary object infront of the vehicle is predicted by the radar control unit 39 (i.e.,when a signal indicating a possibility of a collision with a stationaryobject is sent out), when a collision with a moving object in front ofthe vehicle is predicted by the radar control unit 39 (i.e., when asignal indicating a possibility of a collision with a moving object issent out), and when a collision is predicted by the brake control unit38 based on the pressing rate of the brake pedal (i.e., when the BAsignal is sent out).

Moreover, the electrical seatbelt control unit 35 executes a controloperation such that one of the tensions of differing amounts is appliedto the seatbelt 14 depending on whether a collision is predicted by thebrake control unit 38, a collision with a stationary object is predictedby the radar control unit 39, or a collision with a moving object ispredicted by the radar control unit 39. More specifically, theelectrical seatbelt control unit 35 controls the electric motor 29 so asto exert a tension of F3 when a collision with a stationary object infront of the vehicle is predicted by the radar control unit 39, to exerta tension of F2, which is greater than F3, when a collision with amoving object in front of the vehicle is predicted by the radar controlunit 39, and to exert a tension of F1, which is greater than F3, when acollision is predicted by the brake control unit 38 based on thepressing rate of the brake pedal.

For example, when a collision is predicted by the brake control unit 38,the electrical seatbelt control unit 35 controls electric current beingsupplied to the electric motor 29 so as to fall within a firstpredetermined range (e.g., 10 to 20 A) so that a first predeterminedtension F1 (e.g., 100 N) is exerted on the seatbelt 14. When a collisionwith a moving object is predicted, the electrical seatbelt control unit35 controls electric current being supplied to the electric motor 29 soas to fall within a second predetermined range (e.g., 10 to 20 A) sothat a second predetermined tension F2 (e.g., 100 N) is exerted on theseatbelt 14. When a collision with a stationary object is predicted, theelectrical seatbelt control unit 35 controls electric current beingsupplied to the electric motor 29 so as to fall within a thirdpredetermined range (e.g., 6 to 10 A) so that a third predeterminedtension F3 (e.g., 50 N) is exerted on the seatbelt 14. In this example,the first predetermined tension F1 is set to be the same as the secondpredetermined tension F2; therefore, the first predetermined range ofelectric current is set to be the same as the second predetermined rangeof electric current.

In addition, in either tightening operations based on the prediction ofa collision with a stationary object, based on the prediction of acollision with a moving object, and based on the prediction of acollision at braking, the electrical seatbelt control unit 35 is adaptedto temporarily increase electric current supplied to the electric motor29 at the beginning of controlling of the electric motor 29 for exertingtension on the seatbelt 14 sufficient to restrain the occupant 10 seatedin the seat. More specifically, during a predetermined periodimmediately after the electric motor 29 starts rotation, the limitapplied to electric current is set to be higher than the limit which hasbeen set for exerting a predetermined tension on the seatbelt 14.

This control operation will be further explained with reference to FIGS.4 and 5. When a collision is predicted based on a brake operation,during a predetermined period immediately after the electric motor 29starts rotation, i.e., during a first initial period (e.g., 50 ms) fromtime t21 to time t22 shown in FIG. 4, the limit of electric current isset to be a predetermined first initial limit (e.g., 20 A), and afterthe first initial period, the limit of electric current is set to be apredetermined first limit (e.g., 10 A) which is lower than the firstinitial limit. Moreover, when a collision with a moving object ispredicted, during a predetermined period immediately after the electricmotor 29 starts rotation, i.e., during a second initial period (e.g., 50ms) from time t21 to time t22 shown in FIG. 4, the limit of-electriccurrent is set to be a predetermined second initial limit (e.g., 20 A),and after the second initial period, the limit of electric current isset to be a predetermined second limit (e.g., 10 A) which is lower thanthe second initial limit. Furthermore, when a collision with astationary object is predicted, during a predetermined periodimmediately after the electric motor 29 starts rotation, i.e., during athird initial period e.g., 50 ms) from time t31 to time t32 shown inFIG. 5, the limit of electric current is set to be a predetermined thirdinitial limit (e.g., 10 A), and after the third initial period, thelimit of electric current is set to be a predetermined third limit(e.g., 6 A) which is lower than the third initial limit. In thisexample, the first predetermined tension F1 is set to be the same as thesecond predetermined tension F2; therefore, the first initial limit isset to be the same as the second initial limit, and also the first limitis set to be the same as the second limit. In each of FIGS. 4 and 5, abroken line represents a control target of electric current, and a solidline represents an actual operation electric current.

The electric motor 29 may be controlled so that tension F2 for the casein which a collision with a moving object is predicted is set to begreater than the tension F3 for the case in which a collision with astationary object is predicted, and the tension F1 for the case in whicha collision is predicted based on a brake operation is set to be greaterthan the tension F2 for the case in which a collision with a movingobject is predicted (i.e., F3<F2<F1). In this case, when a collisionwith a stationary object is predicted, the electric current supplied tothe electric motor 29 is controlled so as to fall within a thirdpredetermined range (e.g., 6 to 10 A), when a collision with a movingobject is predicted, the electric current supplied to the electric motor29 is controlled so as to fall within a second predetermined range(e.g., 10 to 20 A), and when a collision is predicted based on a brakeoperation, the electric current supplied to the electric motor 29 iscontrolled so as to fall within a first predetermined range (e.g., 20 to25 A). In this case, the first initial limit is set to be greater thanthe second initial limit, and also the first limit is set to be greaterthan the second limit.

An example of timing of various operations in the seatbelt apparatus 15in the present embodiment along with degree of deceleration will beexplained below in a time-domain manner with reference to FIG. 6.

The radar control unit 39 detects an object in front of the vehicle(e.g., a vehicle) using a radar, and when it is determined that thedistance between the object in front of the vehicle and the vehicle isdecreased to less than a predetermined value based on the radar signals,an automatic braking control operation is started (at time t41 in FIG.6), and a signal indicating a stationary object is output when theobject in front of the vehicle is a stationary object, and a signalindicating a moving object is output when the object in front of thevehicle is a moving object. At the beginning stage of the automaticbraking control operation (from time t41 to time t42 in FIG. 6), theradar control unit 39 gives warning to the occupant 10 that the distancebetween the object in front of the vehicle and the vehicle is decreasedusing a voice message by operating a voice message output device.

Next, when it is determined that a state in which the distance betweenthe object in front of the vehicle and the vehicle is decreased to lessthan a predetermined value is maintained for a predetermined period(e.g., 1 second) despite the voice warning, the radar control unit 39executes a first deceleration control operation in which the radarcontrol unit 39 notifies the occupant 10, through a sense ofdeceleration, that a braking force is generated by operating a brakehydraulic pressure control device so that a braking force for obtaininga predetermined degree of deceleration is generated (from time t42 totime t43 in FIG. 6).

Moreover, when it is determined that a state in which the distancebetween the object in front of the vehicle and the vehicle is decreasedto less than a predetermined value is maintained for a predeterminedperiod (e.g., 0.5 seconds) despite deceleration of the vehicle, theradar control unit 39 executes a second deceleration control operationin which the radar control unit 39 notifies the occupant 10 that abraking force is generated by operating the brake hydraulic pressurecontrol device so that a greater braking force for obtaining apredetermined greater degree of deceleration is generated (from time t43to time t44 in FIG. 6).

On the other hand, when a collision with a moving object in front of thevehicle is predicted by the radar control unit 39, and when theautomatic braking control operation is being executed, the electricalseatbelt control unit 35 receives a signal indicating a moving object.When it is determined, based on the signal indicating a moving object,that a state in which the signal indicating a moving object iscontinuously input is maintained for a predetermined period (e.g., 1second) which is the same as the above-mentioned predetermined periodused for determining beginning of deceleration operation (at time t42 inFIG. 6), the electrical seatbelt control unit 3 5 executes a warningoperation in which a warning is given to the occupant 10 using theseatbelt 14 on condition that the buckle signal output from the buckleswitch 45 is input to the electrical seatbelt control unit 35 via theairbag control unit 43. More specifically, a warning is given to theoccupant 10 by operating the electric motor 29 of the secondpretensioner 30 so that normal rotations by which the seatbelt 14 istightened and reverse rotations by which the seatbelt 14 is loosened arealternately repeated.

As shown in FIG. 2, in the warning operation, the electric motor 29 isoperated in the normal direction for a predetermined first normaloperation period (e.g., 100 ms), the electric motor 29 is stopped for apredetermined first stop period (e.g., 10 ms), the electric motor 29 isoperated in the reverse direction for a predetermined first reverseoperation period (e.g., 50 ms), and then the electric motor 29 isstopped for a predetermined pause period (e.g., 150 ms). Next, theelectric motor 29 is operated in the normal direction for apredetermined second normal operation period (e.g., 100 ms), theelectric motor 29 is stopped for a predetermined second stop period(e.g., 10 ms), the electric motor 29 is operated in the reversedirection for a predetermined second reverse operation period (e.g., 50ms), and then the electric motor 29 is stopped for a predetermined pauseperiod (e.g., 150 ms). Next, the electric motor 29 is operated in thenormal direction for a predetermined third normal operation period(e.g., 100 ms), the electric motor 29 is stopped for a predeterminedthird stop period (e.g., 50 ms), and then the electric motor 29 isoperated in the reverse direction for a predetermined third reverseoperation period (e.g., 100 ms).

Through the above warning operation, exerting tension on the, seatbelt14 by winding the seatbelt 14, i.e., tightening the seatbelt 14, andreleasing the tension on the seatbelt 14 by unwinding the seatbelt 14,i.e., loosening the seatbelt 14, are alternately repeated as shown inFIG. 3, so that a warning is given to the occupant 10 using the seatbelt14. This warning operation is executed substantially simultaneously withthe above-mentioned deceleration control operation (from time t42 totime t44 in FIG. 6). Alternatively, the warning operation may beaccompanied with a visual warning using, for example, a warning lamp,may be accompanied with an audible warning using, for example, a voicemessage output device, or may be accompanied with other type ofwarnings, and these warnings may be combined.

When it is determined that a state in which the distance between theobject in front of the vehicle and the-vehicle is decreased to less thana predetermined value is maintained for a predetermined period (e.g., 2seconds) despite the deceleration control operation and the warningoperation, the radar control unit 39 executes an emergency automaticbraking operation in which the radar control unit 39 controls the brakehydraulic pressure control device so that a greater braking force forobtaining a predetermined greater degree of deceleration is generated(at time t44 or thereafter in FIG. 6).

On the other hand, when a collision with an object in front of thevehicle is predicted by the radar control unit 39, and when it isdetermined, based on a signal indicating a stationary object or a movingobject, by the electrical seatbelt control unit 35, which receives asignal indicating one of a stationary object and a moving object duringthe automatic braking control operation, that a state in which thesignal indicating a stationary object or a moving object is continuouslyinput is maintained for a predetermined period (e.g., 2 second) which isthe same as the above-mentioned predetermined period used fordetermining beginning of the emergency automatic braking operation (attime t44 in FIG. 6), the electrical seatbelt control unit 35 restrainsthe occupant 10 in the seat 13 using the seatbelt 14 by executing atightening operation in which the electric motor 29 is rotated in thenormal direction for a predetermined normal operation period (e.g., 1second) so as to wind the seatbelt 14 for tightening, and then theelectric motor 29 is stopped for at least a predetermined fixing period(e.g., 2 seconds) in order to fix the retractor 20 (i.e., in order notto allow drawing out).

When a signal indicating a stationary object is output during the abovetightening operation, i.e., when a collision with a stationary object ispredicted, the limit of electric current is set to be the predeterminedthird initial limit (e.g., 10 A), i.e., the limit of electric current istemporarily set to be a great value, during a predetermined periodimmediately after the electric motor 29 starts rotation, i.e., duringthe third initial period (e.g., 50 ms), so that the seatbelt 14 isinstantly drawn taut, and after the third initial period, the limit ofelectric current is set to be the predetermined third limit (e.g., 6 A),which is lower than the third initial limit, so that the thirdpredetermined tension (e.g., 50 N) as the tension F3 is exerted on theseatbelt 14. On the other hand, when a signal indicating a moving objectis output during the above tightening operation, i.e., when a collisionwith a moving object (e.g., a proceeding vehicle) is predicted, thelimit of electric current is set to be the predetermined second initiallimit (e.g., 20 A), i.e., the limit of electric current is temporarilyset to: be a great value, during a predetermined period immediatelyafter the electric motor 29 starts rotation, i.e., during the secondinitial period (e.g., 50 ms), so that the seatbelt 14 is instantly, andafter the second initial period, the limit of electric current is set tobe the predetermined second limit (e.g., 10 A), which is lower than thesecond initial limit, so that the second predetermined tension (e.g.,100 N) as the tension F2 is exerted on the seatbelt 14.

After this control operation, when it is determined that, after a brakesignal is output from a brake switch, for example, upon a brakingoperation by the occupant 10 (at time t45 in FIG. 6), the pressing ofthe brake pedal is released and the brake signal is ended, or when it isdetermined that the vehicle speed is zero based on the output signalfrom the vehicle speed sensor, the electrical seatbelt control unit 35operates the electric motor 29 so that the fixing of the retractor 20,i.e., the tightening operation, is cancelled. In FIG. 6, the brokenindicates a degree of deceleration due to the braking operation by theoccupant 10.

On the other hand, when it is determined that the pressing rate of thebrake pedal exceeds a predetermined rate which is determined beforehand,i.e., when it is determined that the braking operation is an emergencybrake operation (at time t51 in FIG. 6), a brake assist controloperation is executed and the degree of deceleration is quicklyincreased (represented by the two-dot chain line in FIG. 6) because acollision with an object in front of the vehicle is predicted. When theelectrical seatbelt control unit 35 receives the BA signal which isoutput during the brake assist control operation, the electricalseatbelt control unit 35 restrains the occupant 10 in the seat 13 usingthe seatbelt 14 by executing a tightening operation in which theelectric motor 29 is rotated in the normal direction for a predeterminednormal operation period (e.g., 1 second) so as to wind the seatbelt 14for tightening, and then the electric motor 29 is stopped for at least apredetermined fixing period (e.g., 2 seconds) in order to fix theretractor 20 (i.e., in order not to allow drawing out).

When a collision with an object in front of the vehicle is predictedbased on the pressing rate of the brake pedal, the limit of electriccurrent is set to be the predetermined first initial limit (e.g., 20 A),i.e., the limit of electric current is temporarily set to be a greatvalue, during a predetermined period immediately after the electricmotor 29 starts rotation, i.e., during the first initial period (e.g.,50 ms), so that the seatbelt 14 is instantly drawn taut, and after thefirst initial period, the limit of electric current is set to be thepredetermined first limit (e.g., 10 A), which is lower than the firstinitial limit, so that the first predetermined tension (e.g., 100 N) asthe tension F1 is exerted on the seatbelt 14.

After this control operation, when it is determined that the pressing ofthe brake pedal is released and the brake signal is ended, or when it isdetermined that the vehicle speed is zero based on the output signalfrom the vehicle speed sensor, the electrical seatbelt control unit 35operates the electric motor 29 so that the fixing of the retractor 20,i.e., the tightening operation, is cancelled. As a result, the seatbelt14 can be drawn out from the retractor 20.

On the other hand, when a collision of the vehicle is detected by thecrash sensor 49, the airbag control unit 43 makes the airbag deployed,and ignites the explosive first pretensioner 28 so that the seatbelt 14is instantly drawn taut.

According to the above-described embodiment of the seatbelt apparatus15, the following advantageous effects can be obtained.

Because the electrical seatbelt control unit 35 exerts one of thetensions of differing amounts in the seatbelt 14 depending on whether acollision with a stationary object is predicted by the radar controlunit 39, a collision with a moving object is predicted by the radarcontrol unit 39, or a collision is predicted by the brake control unit38, and more specifically, the electrical seatbelt control unit 35exerts a greater amount of tension on the seatbelt 14 when a collisionwith a moving object is predicted and when a collision is predicted bythe brake control unit 38 than when a collision with a stationary objectis predicted, a great amount of tension is exerted on the seatbelt 14for ensuring tightening by the seatbelt 14 when a collision with amoving object is predicted and when a collision is predicted by thebrake control unit 38, i.e., when probability of collision is high, anda small amount of tension is exerted on the seatbelt 14 when a collisionwith a stationary object, such as irregularities in the road, ispredicted, i.e., when probability of collision is low. Accordingly, whena collision is predicted and the occupant 10 is to be restrained in theseat 13 using the seatbelt 14, an optimum amount of tension is exertedon the seatbelt 14 depending on the prediction results for a collision,and the occupants will not experience unnecessary unusual sensations.

In addition, at the beginning of the control operation by the electricalseatbelt control unit 35 for exerting tension on the seatbelt 14, theseatbelt 14 can be instantly drawn taut by temporarily increasingelectric current being supplied to the electric motor 29 so that therotational rate of the electric motor 29 is increased.

In the above-described embodiment, the explosive first pretensioner 28and the second pretensioner 30 operated by the electric motor 29 areboth provided in the retractor 20; however, just the explosive firstpretensioner 28 may be provided in the retractor 20, and the secondpretensioner 30 may be provided in the buckle 30. In this case, thesecond pretensioner 30 draws the buckle 26 by being operated by theelectric motor 29 so that the seatbelt 14 is tightened. Alternatively,dispositions of the first pretensioner 28 and the second pretensioner 30may be reversed.

The seatbelt apparatus 15 according to the present embodiment may beapplicable not only at the driver's seat, but also at the passengerseats.

While preferred embodiments of the invention have been described andillustrated above, it should be understood that these are exemplary ofthe invention and are not to be considered as limiting. Additions,omissions, substitutions, and other modifications can be made withoutdeparting from the spirit or scope of the present invention.Accordingly, the invention is not to be considered as being limited bythe foregoing description, and is only limited by the scope of theappended claims.

INDUSTRIAL APPLICABILITY

As described above, according to the present invention, because thecontrol device exerts one of the tensions of differing amounts in theseatbelt depending on the prediction results by the collision predictiondevices, it is possible to exert great amounts of tension on theseatbelt so as to strongly tighten the seatbelt when probability ofcollision is high, and to exert a small amount of tension on theseatbelt so as to moderately tighten the seatbelt when probability ofcollision is low. Therefore, the occupants will not experienceunnecessary unusual sensations.

According to another aspect of the present invention, because thecollision prediction devices include at least two of a stationary objectcollision prediction device for predicting occurrence of a collisionwith a stationary object, a moving object collision prediction devicefor predicting occurrence of a collision with a moving object, and abrake operation collision prediction device for predicting occurrence ofa collision based on an operation of the brake of the vehicle, thecontrol device can exert an optimum amount of tension on the seatbeltdepending on the prediction results predicted by the collisionprediction devices. Therefore, the occupants will not experienceunnecessary unusual sensations.

According to another aspect of the present invention, because thecontrol device is adapted to exert a greater amount of tension on theseatbelt when occurrence of a collision is predicted by the movingobject collision prediction device and when occurrence of a collision ispredicted by the brake operation collision prediction device than whenoccurrence of a collision is predicted by the stationary objectcollision prediction device, a stationary object, such as irregularitiesin the road, is detected, i.e., when probability of collision is low, asmall amount of tension is exerted on the seatbelt, and when a movingobject is detected, or when a collision is predicted by based on abraking operation, i.e., when probability of collision is high, a greatamount of tension is exerted on the seatbelt. Therefore, the occupantswill not experience unnecessary unusual sensations.

According to another aspect of the present invention, because thecontrol device is adapted to temporarily increase electric currentsupplied to the actuator at the beginning of controlling of the actuatorfor exerting tension on the seatbelt, the operation of the actuator canbe accelerated. Therefore, the seatbelt can be instantly drawn taut.

1. A seatbelt apparatus comprising: a seatbelt for restraining anoccupant in a seat of a vehicle; an actuator for tightening the seatbeltat various levels of tension and for loosening the seatbelt; pluralcollision prediction devices for predicting occurrence of a collision;and a control device for controlling the actuator so as to exert one ofthe various levels of tension on the seatbelt depending on theprediction results by the collision prediction devices.
 2. A seatbeltapparatus according to claim 1, wherein the collision prediction devicescomprise at least two of a stationary object collision prediction devicefor predicting occurrence of a collision with a stationary object, amoving object collision prediction device for predicting occurrence of acollision with a moving object, and a brake operation collisionprediction device for predicting occurrence of a collision based on anoperation of the brake of the vehicle.
 3. A seatbelt apparatus accordingto claim 1, wherein the collision prediction devices comprise astationary object collision prediction device for predicting occurrenceof a collision with a stationary object, a moving object collisionprediction device for predicting occurrence of a collision with a movingobject, and a brake operation collision prediction device for predictingoccurrence of a collision based on an operation of the brake of thevehicle, and wherein the control device is adapted to exert a greateramount of tension on the seatbelt when occurrence of a collision ispredicted by the moving object collision prediction device and whenoccurrence of a collision is predicted by the brake operation collisionprediction device than when occurrence of a collision is predicted bythe stationary object collision prediction device.
 4. A seatbeltapparatus according to claim 1, wherein the control device is adapted totemporarily increase electric current supplied to the actuator at thebeginning of controlling of the actuator for exerting tension on theseatbelt.